1. Field of the Invention
The present invention is directed to a method and apparatus for the production of high purity hydrogen gas. The method advantageously produces large volumes of hydrogen gas at a low cost as compared to prior art methods. The hydrogen gas can be used in a number of diverse applications such as for fuel cells and for many different chemical processes such as hydrogenation reactions.
2. Description of Related Art
It is known that hydrogen gas (H2) can be produced from many different feedstocks such as natural gas, biomass or water using a number of different techniques such as reformation, gasification or electrolysis. The most common methods are steam methane reformation, coal gasification, non-catalytic partial oxidation, biomass gasification and pyrolysis, and electrolysis.
Steam methane reformation is believed to be the most economical and commercially viable process that is presently available. The feedstock is typically natural gas and the cost of the natural gas feedstock represents about 52% to 68% of the total cost. The process reacts methane (CH4) with steam (H2O) to form a gas stream that includes H2 and CO and the CO must be separated from the gas stream to form pure H2.
Hydrogen production from coal gasification is another established commercial technology, but is only economically competitive where natural gas prohibitively expensive. In the coal gasification process, steam and oxygen are utilized in the coal gasifier to produce a hydrogen-rich gas. High purity hydrogen can then be extracted from the synthesis gas by a water-gas shift reaction. Other gases such as fuel gases and acid gases must also be separated from the hydrogen. Hydrogen can be similarly formed by the gasification of hydrocarbons such as residual oil.
The manufacture of hydrogen by the reduction of steam using a metal species is also known. For example, U.S. Pat. No. 4,343,624 by Belke et al. discloses a 3-stage hydrogen production method and apparatus utilizing a steam oxidation process. In the first stage, a low Btu gas containing H2 and CO is formed from a feedstock such as coal. The low Btu gas is then reacted in a second stage with ferric oxide (Fe3O4) to form iron (Fe), carbon dioxide (CO2) and steam (H2O) in accordance with the reaction:
Fe3O4+2H2+2COxe2x86x923Fe+2CO2+2H2O
The steam and iron are then reacted in a third stage to form hydrogen gas by the reaction:
3Fe+4H2Oxe2x86x92Fe3O4+4H2
It is disclosed that the iron oxide can be returned to the second stage for use in the iron oxide reduction reaction, such as by continuously returning the iron oxide to the second stage reactor via a feed conduit. At least one of the stages takes place in a rotating fluidized bed reactor.
U.S. Pat. No. 4,555,249 by Leas discloses a gas fractionating unit that contains a reagent powder, such as an iron alloy, having a significant weight difference between the reduced form and the oxidized form. The unit includes two zones for containing the reagent powder, an oxidation zone and a reduction zone, wherein hydrogen gas is extracted from the oxidation zone. As the reagent powder is converted from the oxidized to the reduced form, the weight of the powder increases and the change in weight is utilized to transfer the reduced powder to the oxidation zone while moving the oxidized powder to the reduction zone.
The article xe2x80x9cH2 from Biosyngas via Iron Reduction and Oxidationxe2x80x9d, by Straus et al., discloses a method for hydrogen production from biosyngas. The biosyngas, which included H2, CO, H2O, and CO2 with traces of N2 and CH4, was used to reduce magnetite (Fe3O4) to iron (Fe). The iron was then cooled and fed to a hydrogen gas generator where the iron was contacted with steam to form hydrogen by steam-oxidation. The iron oxide was then cooled and returned to the reduction reactor for reaction with the biosyngas.
Other metal/metal oxide systems have been used in addition to iron/iron oxide. For example, U.S. Pat. No. 3,821,362 by Spacil illustrates the use of Sn/SnO2 to form hydrogen. Molten tin is atomized and contacted with steam to form SnO2 and hydrogen gas. The SnO2 is then contacted with a producer gas composed of H2, N2 and CO, which is formed by contacting powdered coal with air. The SnO2 is reduced to liquid tin, which is then transferred back to the first reactor. A similar method for hydrogen production is illustrated in U.S. Pat. No. 3,979,505.
Despite the foregoing, there remains a need for a method for economically producing large volumes of hydrogen gas.
The present invention is directed to a method for the production of hydrogen gas having a high purity. According to one aspect of the present invention, the method includes the steps of separately generating a reducing gas and steam, contacting the reducing gas with a metal oxide in a first reaction zone to form a metal and contacting the steam with a metal in a second reaction zone to form hydrogen gas by reduction of the steam, yielding a metal oxide. The valve connecting the reactors and the gas generation zones is switched after a period of time such that the reducing gas is contacted with the metal oxide that was formed in the second reaction zone and steam is contacted with the metal that was formed in the first reaction zone to form hydrogen gas. The gas flows can be switched periodically to provide the continuous production of hydrogen gas.
According to one particularly preferred embodiment of the present invention, at least one of the metals is tin and at least one of the metal oxides is tin oxide. According to another preferred embodiment, at least one of the metals is iron and at least one of the metal oxides is iron oxide, preferably FeO. In one embodiment, the steam can be reacted with the metal by injecting the steam into a molten bath of the metal. In another embodiment, the steam can be contacted with solid metal particulates, such as in a fluidized bed.
The method and apparatus of the present invention advantageously enable the economical production of hydrogen gas in large volumes. It is an advantage of the present invention that the non-gaseous reactants are not physically moved during the process nor are the non-gaseous reactants substantially heated, cooled and reheated, which wastes valuable process energy.
The hydrogen production method and apparatus can stand-alone and generate large volumes of hydrogen gas for use, for example, in fuel cells or in chemical processes. Alternatively, the hydrogen production apparatus can be integrated into a chemical reduction process or the like.